The position of a valve element and as a result the through-flow of a medium through a valve can be adjusted via a valve actuator. The valve actuator typically includes an electric motor which is coupled to the valve element via a gear mechanism and a spindle, which valve element is associated with a valve seat in order to control or regulate the through-flow through the valve. Generally, it is desirable to design the valve actuator to be as low in friction as possible, whereby the required displacement forces are reduced and the efficiency of the valve actuator is increased accordingly. This can be achieved, for example, in that the spindle is produced with an extremely high level of quality so that the friction thereof is minimised. Such a spindle is also referred to as a super low friction spindle.
However, it has proved to be disadvantageous that the valve element can be displaced owing to the pressure of the medium, since the low friction spindle does not have a self-locking effect counteracting the opening moment resulting from the pressure of the medium. Therefore, although the valve is highly efficient in terms of displaceability, it cannot be securely held in a desired position.
The object of the invention is to provide a valve actuator which has a high level of efficiency and at the same time the valve can be securely held in an adjusted position.